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Discussion Starter #1 (Edited)
I've put together an Excel spreadsheet (attached) that lets you experiment with changes in final drive ratios (sprockets) and rear tire sizes and see the effects on RPM versus speed. For example, changing the countershaft sprocket from 17T to 16T raises the 70 MPH cruising RPM from 4634 to 4923.

If there's interest, I will post a metric version.
 

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Cool... Thanks for the spreadsheet. Now if only I could make my 10R rev to 15,000 rpm. LOL

So theoretically, with a 16t CS, you'd be pushing about 180mph when bumping off the rev limiter (~12,700 rpm by the looks of most dyno plots)
 

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Discussion Starter #4
Rspec99 said:
So theoretically, with a 16t CS, you'd be pushing about 180mph when bumping off the rev limiter (~12,700 rpm by the looks of most dyno plots)
Doesn't the 10R allow a little overrev?
 

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Crypto -

Nice work on the spreadsheet.

But now I'm a bit confused. When riding the 10R with stock gearing, the speedo indicates about 15mph/1,000rpm, which is also what your spreadsheet shows as calculated. However, we all know that there is factory speedo error of around 6-7%, which would compute to an actual speed of around 14mph/1,000rpm.

I suspect that the discrepancy is with using EXACT numbers for tire width & aspect ratio. Tires don't usually measure out to their stated size, although they're usually only a few mm off so I don't know if that's enough to affect your #'s.

I DO know that when I dialed in my speedo with the Speedohealer, my GPS is showing about 13mph/1,000rpm, WITH -1T in front, which is 1mph/1,000rpm LESS than the spreadsheet shows for 16/39 gearing.

???????????
 

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I've put together an Excel spreadsheet (attached) that lets you experiment with changes in final drive ratios (sprockets) and rear tire sizes and see the effects on RPM versus speed. For example, changing the countershaft sprocket from 17T to 16T raises the 70 MPH cruising RPM from 4634 to 4923.

If there's interest, I will post a metric version.
The amount of tire wear plays a small part as well... Could this be the difference?
 

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Discussion Starter #8
zx9rmal said:
I suspect that the discrepancy is with using EXACT numbers for tire width & aspect ratio. Tires don't usually measure out to their stated size, although they're usually only a few mm off so I don't know if that's enough to affect your #'s.

I DO know that when I dialed in my speedo with the Speedohealer, my GPS is showing about 13mph/1,000rpm, WITH -1T in front, which is 1mph/1,000rpm LESS than the spreadsheet shows for 16/39 gearing.
I wouldn't trust GPS figures at low speeds, since the position accuracy is only around 15 meters and you aren't getting enough of an averaging effect. The calculations are based on theoretical tire sizes, and I know from experience that manufacturers don't always stick to exact sizes. Plus, wear, inflation level and rider weight probably all have an effect on effective diameter. Perhaps I should add a tire correction factor to the spreadsheet.
 

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Discussion Starter #11
Ok, I added a tire-correction field. You can adjust the number until it agrees with your GPS then play whatifs from there.
 

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Cryptoman said:
Ok, I added a tire-correction field. You can adjust the number until it agrees with your GPS then play whatifs from there.
Excellent! I'm sure that tire wear has a significant effect, but, again, the speedo is programmed to read 15mph/1,000 rpm stock, i.e., new bike/tire. I'm gonna stick with my Garmin GPS V readings, then check them with radar and mile post signs. I'll report back.
 
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